Zoom, zoom, and zoom

In brief: there is wide support for three different types of ‘zoom’ – available both to site visitors and (to some extent) CSS authors:

Page zoom is the default with a handy keyboard shortcut, and roughly matches behavior of the CSS zoom property.

Scale factor (or ‘pinch zoom’) was introduced by early versions of mobile Safari, and may only be available through trackpad or touch interfaces – roughly matching the behavior of the CSS scale transform.

Text-only zoom is also provided by Firefox and Safari. While not directly available in CSS, the behavior is similar to changing default font size on a site that uses entirely relative text sizing with rem units.

Source: Zoom, zoom, and zoom | OddBird